‘MASS’ TRANSIT: Commuters yesterday pack the Bowling Green station after getting off the 4 train, one of the most crowded lines.NY Post: Chad Rachman

Two of the most overcrowded lines in the subway system have been squeezing in even more riders, thanks to Hurricane Sandy.

Straphangers are packing in to the 4 and 5 trains like sardines since the R train stopped running between Manhattan and Brooklyn, transit officials said yesterday.

The extreme conditions — which together carry about 1.07 million passengers a day — have transit officials scrambling to repair the R line’s Montague Street tunnel, which has been closed since it was damaged in the storm.

Because of the closure, R trains cannot run under the East River, forcing many of its riders onto the 4 and 5 trains, which run a similar route in Downtown Brooklyn and Lower Manhattan.

“The 4 and the 5 are getting hammered,” Thomas Prendergast, president of New York City Transit, said at the agency’s transit committee meeting.

“Everybody who comes across from the [Staten Island] ferry who normally takes the R is walking up to the 4 and 5 at Bowling Green.”

In Brooklyn, R train riders are switching at Atlantic Avenue to the 4 or 5 to cross the East River, Prendergast added.

The R isn’t running between Jay Street-MetroTech and 34th Street in Manhattan.

Fixing the tunnel is the agency’s “highest priority,” Prendergast said, adding he hoped service will be back in seven to ten days.

Transit workers are toiling run the clock to get it down, he said.

The first step will be extending the R in Manhattan down to Rector, he said.

But even if the R trains do end up going to Brooklyn soon, it’s possible the crush conditions will continue on the 4 and the 5.

That’s because the Whitehall Street station — which is near the 4 and 5’s Bowling Green stop and serves many Staten Island ferry riders — is nowhere near ready to open, said Prendergast.

“We do not know when we’ll be able to use Whitehall as a station stop,” he said.

R trains will likely skip that station when service is restored between Brooklyn and Manhattan, he said.

In addition, the South Ferry 1 train station — which was so flooded that its staircase caved in and the elevators were destroyed — will take “months” to be back in service, Prendergast said.

And in more bad news for riders, MTA board member Andrew Albert asked MTA officials to consider reimbursing unlimited MetroCard riders who lost rides during Sandy.

But the request was met with little enthusiasm yesterday.

The MTA, however, wants its money back.

The agency is asking the feds for $124 million in lost revenue for a five day, post-storm stretch when the system was either completely or partially shut down.

It’s also asking for $410 million for repairs to the Brooklyn Battery Tunnel, and $359 for the Queens-Midtown Tunnel, and $3.5 million for the Second Avenue Subway.

MTA officials are also looking into new ways of preventing future storm damage — like using massive balloons to close off subway tunnels.